Low fat spreads which have been generally on the market for several years are fat-continuous emulsions having a fat content of around 20 to 40%. EP-A-0256712 and EP-A-0327225 of the present applicants disclose water-in-oil emulsion low fat spreads with a fat content of 18 to 35%, in which small amounts of modified starch are added to milk protein-containing aqueous phases. As the starch content is increased, the protein content of the aqueous phase can be decreased. This allowed the production of milk-protein-containing low fat spreads of 25% fat content.
Various attempts have also been made to produce water-continuous low fat spreads having a very low fat content, i.e. less than 20% fat. Very low fat milk protein-containing water-continuous emulsions are disclosed in the following documents although not all of the emulsions are useful for spreading on bread as a substitute for butter or margarine: EP-A-0340857, EP-A-0283101, EP-A-0441494, EP0509707, GB-A-2229077, and FR-A-2580471. Besides these documents, there are at least three water-continuous very low fat spreads on the market in the UK, two of which contain only 5% of fat, and one contains only 3% of fat.
As a further example, EP-A-0298561 discloses edible plastic dispersions which may be formulated as very low fat spreads which are water-continuous emulsions. In order to form these plastic dispersions, two gelling agents are required, at least one of which must be an aggregate-forming gelling agent. A key feature of EP-A-0298561 is the requirement to formulate the edible dispersions so that they have a defined plastic rheology. EP-A-0298561 uses the known rheological technique of compression analysis (see for example Dairy Rheology:A Concise Guide, by J. H. Prentice, published by VCH Publishers, 1992) to analyse the stress/strain characteristics of the dispersions produced.
Referring to FIG. 1 of the present application, a graph of stress vs. strain is shown for ideal product behaviour under compression analysis for each of the following products: a hydrocolloid gel, a plastic dispersion, and a viscous solution.
The characterising features of the stress/strain profile are as follows:
the maximum stress (.sigma.max), which is the point where the stress goes through a maximum value (this may in practice be a shoulder on the profile rather than a peak); PA1 the maximum strain (.epsilon.max), which is the strain at the maximum stress (.sigma.max); PA1 the plastic stress (.sigma.p), which is the stress at a horizontal or near-horizontal portion of the curve at a strain slightly larger than the maximum strain; and PA1 the inflectional stress (.sigma.i), which is the point where the stress goes through a minimum value at a strain larger than the maximum strain. PA1 acidifying the heated preparation, for example by the use of a suitable starter culture or by the addition of a suitable organic acid such as lactic acid or by the addition of a suitable mineral acid; PA1 separating the protein by centrifugal separation or by ultrafiltration. This method is described in further detail in GB-1455146, GB-A-2011942, and GB-A-2020532. (4) Mixing and heat treating a solution of caseinates and whey protein preparations in which the proportion of caseinates to whey proteins is the same as the proportion of casein to whey proteins in milk.
The ratio of the plastic stress to the maximum stress (.sigma.p/.sigma.max) of a plastic dispersion will clearly be much greater than the ratio of the inflectional stress to the maximum stress (.sigma.i/.sigma.max) of a hydrocolloid gel. The maximum strain (.epsilon.max) for hydrocolloid gels will occur over a wide range of strain values (0.1 to 1.0) depending on the elastic or brittle nature of the gel network. Viscous solutions produce a smooth stress/strain profile with no apparent signs of yield points on the curve during the compression cycle.
According to EP 0298561, the ratio of the plastic stress to the maximum stress (.sigma.p/.sigma.max) is preferably 0.2 to 0.95, more preferably 0.3 to 0.8.
It is highly important in the field of low fat spreads to generate products of good spreading properties; these will have textural profiles closely resembling the stress-strain relationship illustrated for the idealised plastic dispersion of FIG. 1. It is generally recognised by those skilled in the art that two of the spreadable foods showing the most favoured spreading properties are butter and a full fat soft cheese, such as that known by the trade name of "Philadelphia". These products are respectively a fat-continuous emulsion and a water-continuous emulsion, and both show stress-strain profiles similar to the idealised plastic dispersion of FIG. 1. None of the very low fat spreadable products available on the market exhibits rheological parameters comparable to those of the idealised plastic dispersion of FIG. 1.